1. Field of the Invention
This invention relates to a process for preparing a novel supported vanadium catalyst which may be employed with a cocatalyst for use in the polymerization of olefins to polyolefins. The process comprises reacting a supported vanadium catalyst composition with a phosphine compound, in variable amounts, to produce a novel supported vanadium catalyst which catalyzes the polymerization of olefin monomers to produce a polyolefin the molecular weight distribution of which is controlled as a function of the P/V mole ratio of the catalyst.
2. Background Information
The use of vanadium-based catalysts in the polymerization of olefins is well known.
When produced without a support, vanadium catalysts usually assume the form of an oil or gum. As a consequence, unsupported vanadium-based catalysts are unsuitable for use in a slurry or gas phase reaction procedure by which a polymer product may be produced directly in particle form. Unsupported vanadium-based catalysts are not suited for slurry or gas phase polymerization procedures because the oil or gum form of the unsupported catalyst causes reactor fouling.
U.S. Pat. No. 3,278,643 of Achon teaches the copolymerization of ethylene with 1-olefins using a catalyst which consists of a vanadium oxytrichloride, an alkylaluminum dihalide, and an organic phosphorous compound. The patent does not teach how to obtain the catalyst in a particulate form so as to permit use of the catalyst in a gas or slurry phase polymerization process and does not teach any method to produce a wide range of molecular weight distribution.
U.S. Pat. 4,233,182 teaches the polymerization of olefins with a catalyst formed from a transition metal compound, an organometallic promoter, an oxygenated phosphorous compound, a divalent metal halide, and an aluminum compound. This patent does not, however, teach how to control the molecular weight distribution (MWD) of the resin produced.
To overcome the reactor fouling problem U. S. Pat. No. 4,514,514 by Martin, teaches a process for polymerizing ethylene in the presence of a solid, unsupported catalyst consisting of a vanadium compound, a phosphorous compound, and an organoaluminum compound. The catalyst is highly active and offers some control over the phosphorous compound. Martin's process produces the catalyst precursor as an "oily mass" in certain halogenated hydrocarbon solvents which is thereafter precipitated to a solid catalyst composition by addition of ethylaluminum dichloride (EADC). The use of a halogenated hydrocarbon solvent as the medium in which to react a vanadium compound with an organo-phosphorous compound to produce a product which may be precipitated in solid form by an EADC addition step is a critical aspect of Martin's invention.
U.S. Pat. No. 4,507,449, also by Martin, teaches a polymerization process for the formation of polyethylene using an unsupported solid form of catalyst consisting of a vanadium compound, a phosphorous compound, and a metal halide. The metal halide is a necessary component of the invention in order to form the catalyst in solid particulate form.
It is worth noting that in order to obtain a solid catalyst which may be used in gas or slurry phase reactors, the Martin catalysts require the use of a halogenation agent or a metal halide. This is not desirable since it increases the level of residual halogen in the polymer product which correspondingly leads to increased corrosivity of the polymer product. This problem may, of course, be solved by a deashing step in which catalyst residue is separated from the product. However, a catalyst deashing step increases to cost of producing the polymer product.
An alternative process which provides a solution to both the reactor fouling and the halogen corrosivity problems, is to place a vanadium catalyst composition on a support material. In supported form the vanadium catalyst can be used in a gas or slurry phase processes without encountering reactor fouling. However, it is well known in the art that supported forms of vanadium catalysts present problems of their own. The most significant of these problems is the inability to closely control the MWD of the polymer produced. Generally, supported vanadium catalysts produce a polymer having a broad MWD, the polymer product therefore will include a significant amount of low molecular weight oligomers. These oligomers, when present in polymers used in the manufacture of blow molded articles, produce an unacceptable amount of smoke.
It would be desirable to have a supported vanadium catalyst which could be used in a gas or slurry phase polymerization process to produce in combination with a diene a polyolefin resin of narrower MWD for use as a blow molding resin as described, in co-pending U.S. application Ser. No. 07/981,208.
Yet other applications, such as the manufacture of high density polyethylene (HDPE) films, a high molecular weight resin having a broader MWD is desired. For other resin applications, such as injection molding or linear low density polyethylene (LLDPE) film production, a resin having a narrower MWD is desired. In yet other applications such as wire and cable coatings manufacture, it is desirable for the resin to have a MWD of intermediate breadth.
It would be desirable to have a supported vanadium catalyst for gas or slurry phase production of high molecular weight polyolefins having a MWD which is controllable between broad to narrow, as desired depending on the intended end use of the resin product. A clear need exists in industry for a supported vanadium catalyst which can be tailored to provide resins of a specific MWD over a wide molecular weight range, which will be substantially non-fouling in use, and which will provide a non-corrosive polymer without requiring a deashing step.